1. Field of the Invention
This disclosure describes a high bandwidth, dynamically rigid metrology system (DRMS) for the measurement and control of industrial processes. The phrase "dynamically rigid system" is defined to mean one which establishes a fixed coordinate system in space that, from a functional standpoint, is rigidly attached to a "workpiece" without the need for massive, stiff structures to maintain rigidity. The coordinate system is established by optical means, and the optical devices used in this system have sufficient bandwidth so as to counter the effects of vibration and relative motion between the metrology system and the workpiece. By maintaining a fixed relationship in space between dynamically stabilized laser beams and the workpiece, the functional equivalent of rigidity is attained.
A major feature of this invention is that it can attain very high accuracies in an economical manner by utilizing off the shelf industrial components, often in innovative ways not originally envisioned by the manufacturer. Therefore, the costs for obtaining high performance are reduced substantially, often to one percent or less of the cost associated with the current state of the art.
In some cases, there are relatively large errors associated with certain classes of industrial components, and these cannot be reduced to acceptable tolerances regardless of cost. The environment in which this invention is used also induces errors in positioning, and these errors must be measured. An integral part of this invention is the means of measuring these errors, and correcting them. Substantial computational power such as that provided by workstations or high end personal computers is required to execute the high speed mathematical operations used to compute corrections in real time. In addition, reduced noise optical sensors and improved light sources enable low-cost, precision sensing and tracking.
2. Description of the Related Art
COMPETING APPROACHES
Metrology approaches can be classified as either direct or indirect. A direct measurement is made, for example, by measuring the position of a point with respect to some reference with a tape measure. An example Of the indirect measurement approach is a stereoscopic vision system where the distance measurement is made by triangulation. The quantities actually measured are the distance between two cameras and the registration of the images on the focal plane. The dynamically rigid metrology system (DRMS) of the present invention is an indirect measure method. Table I illustrates the competing technologies with DRMS.